In optical fiber connecting technology, there is known an optical connector provided with, at a common connector body, a ferrule for securely supporting an optical fiber having a predetermined length (in the present specification, called an “incorporated optical fiber”) and a splicing section near the ferrule and able to operate for gripping under pressure a part of the incorporated optical fiber projecting out from the ferrule and an optical fiber of an optical fiber cable introduced from the outside (for example, see Japanese Patent No. 3445479). This type of optical connector with a splicing section is being used often as being able to easily form a connection part of an optical transmission line able to be freely connected and separated in particular at the installation site of the optical transmission line.
An optical connector with a splicing section is generally formed with the front end face of the incorporated optical fiber secured in the fiber holding channel of the ferrule made smooth by polishing the abutting end face of the ferrule (that is, the face which will abut against the ferrule of the other optical connector) in advance in the connector production plant or other facility and with the rear end face of the projecting portion of the incorporated optical fiber projecting out from the other end of the ferrule made smooth by slicing using a cutting tool. Further, the splicing section is provided with a fiber securing member provided with a straight securing groove able to be arranged coaxially with respect to a fiber holding channel of the ferrule so as to be able to operate between a closed position securely gripping the projecting portion of the incorporated optical fiber in the securing groove and an open position releasing that projecting portion. When the optical connector is not being used, the projecting portion of the incorporated optical fiber projecting from the ferrule is received in the securing groove of the fiber securing member of the splicing section at the open position or closed position and arranged at a predetermined centering position.
Said optical connector can be attached to the terminal end of an optical fiber cable with a high precision and low loss by performing the required cable terminating operation and splicing operation on the optical fiber cable to be attached at the installation site of an optical transmission line. Specifically, as the cable terminating operation, the sheath is stripped off a desired length of the terminal end of the optical fiber cable to expose the covered optical fiber, the covering is stripped off a desired length of the terminal end of the covered optical fiber to expose the optical fiber, and the exposed optical fiber is sliced to a predetermined length by a cutting tool. Further, in the splicing operation, the fiber securing member of the splicing section of the optical connector is set to the open position, the exposed optical fiber of the optical fiber cable is inserted in the securing groove of the fiber securing member, the sliced end face of the cable optical fiber is made to abut against the rear end face of the projecting portion of the incorporated optical fiber in the securing groove, and in that state the fiber securing member is moved to the closed position. Due to this, the incorporated optical fiber and the cable optical fiber are securely supported in a concentric end-abutting condition, whereby the optical connector is attached to the optical fiber cable.
Here, at the time of the splicing operation, before moving the fiber securing member of the splicing section from the open position to the closed position, it is necessary to make the incorporated optical fiber and the optical fiber of the optical fiber cable accurately abut against each other at their end faces. This accurate abutting condition is secured by bringing the incorporated optical fiber and the cable optical fiber into contact at their end faces in the securing groove of the fiber securing member, then applying a suitable pressing force in the lengthwise direction toward the fiber securing member to the covered optical fiber of the optical fiber cable. At this time, the covered optical fiber is bent somewhat at the outside of the fiber securing member due to the pressing force in the lengthwise direction. Further, a special assembly tool has been proposed in the past which can hold the covered optical fiber of the optical fiber cable in the bent state so as to maintain the pressed abutting state of the end faces of the optical fibers while moving the fiber securing member from the open position to the closed position until finishing the splicing operation (for example, see Japanese Unexamined Patent Publication (Kokai) No. 2002-23006).
The assembly tool described in JP Kokai 2002-23006 is provided with a connector mount for mounting the body of an optical connector, an operating part for operating the fiber securing member of the optical connector, and a fiber holding part for holding the covered optical fiber of the optical fiber cable at a predetermined position with respect to the optical connector—all suitably arranged on a single base. The fiber holding part is provided with a gripping member comprised of a sponge or other elastic material and can grip the covered optical fiber by a suitable elastic force in a slit provided in the gripping member. At the time of a splicing operation of the optical connector, the optical fiber exposed at the terminal end of the optical fiber cable is inserted into the fiber securing member of the optical connector mounted at the connector mount, then the covered optical fiber is inserted into the gripping member of the fiber holding part while applying a suitable pressing force in the lengthwise direction toward the optical connector to the covered optical fiber. In this state, the covered optical fiber is suitably bent between the optical connector and the gripping member. Due to this, it is confirmed that the incorporated optical fiber and the optical fiber of the optical fiber cable are made to accurately abut against each other in the securing groove of the fiber securing member (normally not visible). Therefore, by moving the fiber securing member from the open position to the closed position while maintaining the bent state of the covered optical fiber, the two optical fibers can be made to connected accurately abutting against each other.
Note that in the present specification, the “covered optical fiber” means a member including a soft covering on the outer surface of the cladding of an optical fiber, while the “optical fiber” means a member stripped of this covering. Further, an “optical fiber cable” means a member including one or more covered optical fibers accommodated together with a tension member in a sheath (generally a plastic sheath), and includes an “optical fiber cord” as well in its broad definition.
Incidentally, in an optical transmission line, an optical fiber connecting system using optical connectors is required to be able to maintain a suitable optical connection condition against any external force such as tension applied to the optical fiber cable. In particular, to prevent the spliced portion of the optical fiber cable and an optical connector from damage due to tension or other external force, there is known an optical connector comprised of a connector body provided with a cable holding part able to securely hold the optical fiber cable (for example, see Japanese Utility Model Registration No. 3022015).
The optical connector described in JP UM 3022015 has, as a cable holding part, a securing member having a U-groove portion able to be arranged in a fiber passage provided in the connector body and movably attached to the connector body. At the time of a splicing operation, the securing member is set at a position on the connector body opening the fiber passage, the end portion of the optical fiber cable is inserted in the fiber passage, then the securing member is pushed into the fiber passage to insert the sheath of the optical fiber cable into the U-groove portion under pressure. Due to this, the optical fiber cable is securely held at the connector body. At this time, a special tool having a cable receiving part is used, the cable receiving part is pushed into the fiber passage of the connector body from the opposite side to the securing member, the optical fiber cable is gripped between the securing member and the cable receiving part, and the optical fiber cable is inserted into the U-groove portion of the securing member.
Here, an optical fiber cable, comprised of one or more covered optical fiber and a pair of tension members (for example, steel wires, FRP (fiber reinforced plastic) cords, etc.) arranged at both lateral sides of the covered optical fiber, which are accommodated in a plastic sheath with substantially no clearance therebetween, is known as a drop optical fiber for an aerial access line (for example, see Japanese Kokai No. 2001-83385). The conventional drop optical cable has a pair of channels extending in the lengthwise direction at opposite positions on the outer surface of the sheath, and, at the time of the cable terminating operation of the drop optical cable, it is possible to tear apart the sheath in the lengthwise direction along the pair of channels so as to easily expose the covered optical fiber.
Conventionally, when attaching an optical connector to the terminal end of such a drop optical cable, the pair of tension members of the terminated drop optical cable are mechanically secured to the connector body by a securing member provided at the optical connector (for example, see Japanese Kokai No. 2003-177275). The optical connector described in JP 2003-177275 is provided at the end at the fiber introduction side of the connector body with a securing member having a passage for the covered optical fiber and a friction area at the outer surface positioned around that passage. The drop optical cable is securely connected to the body of the optical connector by inserting the covered optical fiber into the passage of the securing member to secure it to the ferrule, then arranging the pair of torn apart sheath portions containing the tension members to follow along the friction area at the outer surface of the securing member and tightening a metal fitting from the outside of the two sheath portions to press against the friction area under pressure.
Note that in optical fiber connecting systems using optical connectors, there is known a configuration using a pair of optical connectors having engaging parts of different shapes complementarily engageable with each other at their bodies (so-called “plug” and “socket”). For example, in access work for extending and laying optical fiber cables from a public optical fiber network to individual houses, generally socket-type optical connectors attached to the terminal ends of optical fiber cables are provided at switchboxes provided at desired positions in the houses in accordance with household electrical wiring work. Further, the optical terminals used in houses and optical connectors in the switchboxes are configured so as to be detachably attached using optical fiber cords provided with plug-type optical connectors at their front ends.
In such an application, when installing an optical connector in a limited space such as a switchbox, it is sometimes necessary to lay the optical fiber cable extended from the rear end of the optical connector bent by a large amount near the optical connector. At this time, from the viewpoint of suppressing optical loss, there is proposed an optical connector provided with a cable holding part for holding the optical fiber cable in a state bent to a predetermined radius so as to prevent the covered optical fiber from being bent by a radius smaller than the prescribed smallest bending radius (in the present specification, called an “angle type optical connector”) (for example, see Japanese Kokai No. 2003-161863). As opposed to this, an optical connector without spatial restrictions such as a plug-type optical connector to be attached to an optical fiber cord is provided with a cable holding part for holding the optical fiber cable straight with respect to the ferrule, so is called a “straight type optical connector” in the present specification.